Formulations of clomazone are known and are available commercially. One commercial formulation of clomazone is a solvent-based emulsifiable concentrate (EC). The formulation is typically prepared by dissolving the clomazone active ingredient in an inert organic liquid solvent, together with an appropriate emulsifier system. Mixing the resulting combination with water, spontaneously forms an oil in water emulsion of the clomazone/solvent solution.
Modern agricultural practice requires improved control in the application of biologically active components to the target plants. This improved control in turn provides for a number of advantages. First, the improved control of the active ingredient allows compounds to be used that have an increased stability over extended periods of time. Further, the improved control leads to a reduction in the environmental hazard presented by the herbicidal composition. In addition, improved control leads to a decrease in the acute toxicity of the composition and allows any incompatibility between ingredients to be accommodated.
It is known that microencapsulation is a technique that offers a number of advantages in improving the control achievable in the delivery of herbicidal formulations, compared with other formulation techniques in the field of agrochemicals. Several basic processes for the preparation of microencapsulation formulations of herbicidally active compounds have been disclosed and are known in the art. In particular, known techniques for microencapsulation include coacervation, interfacial polymerization and in-situ polymerization. Most commercially available CS (microcapsule suspension) formulations are manufactured by interfacial polymerization. Examples of commercial CS formulations prepared in this manner include Chlorpyrifos CS, Lambda-cyhalothrin CS, Fluorochloridone CS, and Methylparation CS. When such formulations are dried, they form water dispersible granules containing microcapsules, with the active ingredient being contained within the microcapsules. The microcapsules act to contain the active ingredient, such that when the formulation is applied, for example as a dispersion in water, the active ingredient is released slowly from the microcapsules and its spread outside the locus of application is limited.
Clomazone, (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) is a well-known herbicide for controlling soybean, cotton, cassava, corn, rapeseed, sugar cane, tobacco and other crops. It is known in the art to formulate clomazone by microencapsulation. However, due to the physical properties of clomazone, for example its high volatility, determining the optimum formulation is still highly demanding.
For example, U.S. Pat. No. 6,380,133 discloses a technique to encapsulate clomazone in microcapsules having a shell of a cross-linked polyurea. However, control of the release rate of clomazone is still not satisfactory.
One known method of preparing a CS formulation is by interfacial polymerization. In this method, the active ingredient is dissolved in a solvent, together with monomers and/or prepolymers. The resulting mixture is dispersed into a water phase containing one or more emulsifiers, optionally one or more protective colloids and, optionally, additional prepolymers. A capsule wall is formed around the oil droplets as a result of interfacial polymerization occurring at the oil/water interface in the presence of a catalyst or by heat.
Solvents, although generally inert in the finished formulation, are used in the microencapsulation of active ingredients to perform a number of roles, for example dissolving the active component to allow encapsulation of solid active ingredients, and adjusting the diffusion rate of the active substance through the polymeric wall, in turn aiding in controlling the release of the active ingredients from the microcapsules when the formulation has been applied. In addition, solvents may be selected, in addition to their role of dissolving the active components, to influence the emulsion quality, for example by maintaining a low viscosity during the emulsification and/or polymerization steps.
EP 1 652 433 describes a herbicidal formulation comprising an aqueous liquid composition having suspended therein a plurality of solid microcapsules, the microcapsules having a capsule wall of porous condensate polymer of at least one of a polyurea, polyamide or amide-urea copolymer. The microcapsules are formed to encapsulate clomazone as the active ingredient. Within the capsules, the clomazone is dissolved in a high boiling inert organic solvent, in particular a 1,2-benzenedicarboxylic di-(C3-C6) branched alkyl ester.
EP 0 792 100 describes a process for preparing an encapsulated clomazone formulation. The process involves a step of providing a water immiscible liquid phase consisting of clomazone and polymethylene polyphenyl isocyanate, with or without an aromatic hydrocarbon solvent. EP 0 792 100 describes the microencapsulation of clomazone by preparing a water-immiscible phase containing specified amounts of clomazone and polymethylene polyphenyl isocyanate (PMPPI), together with an aromatic solvent. The solvent is indicated to be optional in the case of formulations with high loadings of clomazone. However, the exemplified formulations generally contain a petroleum solvent in an amount of from 4 to 6% by weight.
EP 1 840 145 discloses a microencapsulated formulation of clomazone, in which the clomazone is dissolved in a solvent, in particular cyclohexanone and retained with microcapsules having a shell formed from a polymer prepared by interfacial polymerization involving the reaction of an isocyanate with an acetylene carbamide derivative.
U.S. Pat. No. 5,783,520 describes a process for preparing an encapsulated clomazone formulation. The process involves a step of providing a water immiscible liquid phase consisting of clomazone and polymethylene polyphenyl isocyanate (PMPPI), with edible oils, such as soy bean oil, corn oil, sunflower oil, as a high boiling organic solvent. U.S. Pat. No. 5,783,520 describes the microencapsulation of clomazone by preparing a water-immiscible phase containing specified amounts of clomazone and PMPPI, together with an edible oil. The formulation is alleged to reduce the volatility of clomazone in the completed formulation.
More recently, US 2014/0031231 discloses a wide range of different formulations of clomazone, with microencapsulated formulations being one of the many suggested. A wide range of organic solvents, including but not limited to a range of animal or vegetable oils, for clomazone is suggested. Linseed oil is specifically exemplified in US 2014/0031231 as a solvent for clomazone.
There is a need for an improved clomazone formulation, in particular an improved microencapsulated clomazone formulation.